Stereotaxic Radiosurgery is the delivery of a focused, large dose of radiation in a single treatment with millimeter precision. It is well tolerated and can be performed as an outpatient procedure. Radiosurgery is highly effective against intracranial tumors. The steep dose gradient resulting from this technique provides a unique opportunity to study in-situ tumor radiobiology. In this pilot study of Radiosurgery, magnetic resonance spectroscopy and perfusion studies will be obtained to describe in-situ metabolic responses to Radiosurgery. In addition to other measures, prospective neuropsychological assessments will be obtained and will be correlated with magnetic resonance spectroscopy. This study is closed to new patients and is open for follow up only.